Dust Over Southwestern Alaska

“Dust in the wind” is a phrase that is used to suggest insignificance. But dust has consequences. Severe dust storms can clog road traffic and send cars to the repair shop; it can clog lungs and send people to the emergency room; it can clog the skies and block sunlight.
Regions rich in sand and waterborne sediments experience frequent dust storms, but dust can easily travel far from its source. Soils in the Amazon rainforest, for example, owe part of their existence to the Bodele Depression on the other side of the Atlantic. Asian dust often migrates across the Pacific Ocean to North America. But while dust can travel great distances, it can also linger in the same region where it originated.
Dust plumes hovered over the ocean off southwestern Alaska in early November 2012. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite observed dust over Bristol Bay on November 6, and dust over the Gulf of Alaska on November 7. While the dust over the Gulf of Alaska could easily be traced to sediments along the Copper River, the source of the dust over Bristol Bay was not as obvious.
Glaciers are common in the region, and as they slowly grind over rocks, they wear away sediment. Meanwhile, river levels rise and fall with the seasons. In the autumn, river levels are falling, and sparse snow cover leaves glacial flour exposed and available for dust storms, which are common between late October and mid-November. “Something like 75 percent of the freshwater to the Gulf of Alaska comes from small, coastal rivers,” explained John Crusius of the U.S. Geological Survey at University of Washington, “and all of these rivers draining ‘glacierized’ landscapes would have deposits of glacial flour at this time of year.” The dust blowing away from the Copper River is an example of a dust storm arising from a regional source.
The dust over Bristol Bay, however, might have had a more distant origin. Santiago Gassó of Goddard Earth Sciences Technology & Research—who studies dust plumes in the Gulf of Alaska to better understand sources of iron in the ocean—was struck by the width of the Bristol Bay plume, as opposed to the relatively narrow plume blowing from the Copper River. Gassó saw the wide and diffuse plume over Bristol Bay and doubted that it could have a local source. ”It might be pollution and dust from China,” he said. Thick dust and smog frequently fills the skies over eastern China at this time of year. (A tundra fire in southwestern Alaska might also have contributed smoke to the plume.)
Colin Seftor of NASA’s Suomi NPP Ozone Science Team took a step further toward a specific source. In early November 2012, severe dust storms struck the Taklimakan Desert of western China. For several days, thick dust blew out of that desert toward the east. The Ozone Mapping Profiler Suite (OMPS), which also tracks aerosols from the Suomi NPP satellite, made observations from November 2 through 8 that show dust traveling east from the Taklimakan Desert, across China, and across the Pacific Ocean.
Credit: NASA image courtesy Jeff Schmaltz, LANCE MODIS Rapid Response Team at NASA GSFC. Caption by Michon Scott.